Solid ink or phase change ink printers conventionally receive ink in a solid form, either as pellets or as ink sticks. The solid ink pellets or ink sticks are placed in a feed chute and a feed mechanism delivers the solid ink to a heater assembly. Solid ink sticks are either gravity fed or urged by a spring through the feed chute toward a heater plate in the heater assembly. The heater plate melts the solid ink impinging on the plate into a liquid that is delivered to a print head for jetting onto a recording medium. U.S. Pat. No. 5,734,402 for a Solid Ink Feed System, issued Mar. 31, 1998 to Rousseau et al. and U.S. Pat. No. 5,861,903 for an Ink Feed System, issued Jan. 19, 1999 to Crawford et al. describe exemplary systems for delivering solid ink sticks into a phase change ink printer.
In known printing systems having an intermediate imaging member, such as ink printing systems, the print process includes an imaging phase, and a transfer phase. In ink printing systems, the imaging phase is the portion of the print process in which the ink is expelled through the piezoelectric elements comprising the print head in an image pattern onto the imaging drum or other intermediate imaging member. The transfer or transfix phase is the portion of the print process in which the ink image on the imaging drum is transferred to the recording medium.
In printers with an imaging member in the form of a rotatable drum, a release agent is often applied to the imaging member before the ink or other marking material that forms the image is transferred to the imaging member. The release agent is typically an oil or similar material such as a silicone fluid that facilitates release of the ink drops or other marking material from the imaging drum and on to the recording medium.
With reference now to FIG. 6 an exemplary embodiment of a presently known release agent application system is shown. In this embodiment, the release agent is deposited on to the imaging drum 200 by a counter-rotating oiling roller 202 before the image is laid down by the print head. The oiling roller 202 dips into a reservoir 204 of release agent and transfers the release agent to the rotating imaging drum 200. Once the release agent is deposited onto the imaging drum 200, the thickness of the release agent on the imaging drum is controlled by a flexible metering blade 206. The flexible metering blade 206 is designed to scrape excess oil away from the imaging drum 200 as it passes the metering blade 206. Thereafter, a print head applies an image to the metering drum on top of the release agent. Once the image is properly printed on the drum 200, the transfix process occurs between paper and in a high pressure nip formed by a transfix roller (not shown in FIG. 6) and the imaging drum 200. However, if too much release agent is metered onto the imaging drum 200, the excess release agent may be transferred to the print media, and the print media may contaminate the transfix roller.
The presence of release agent on the transfix roller typically does not affect printing for one-sided images, as the release agent is only on the side of the media sheet to which no image was transferred. However, in duplex or two-sided printing, the presence of release agent may degrade the quality of the image. This degrading occurs because the release agent on the back side of the media sheet affects the transfer of ink from the imaging member to the media sheet. Consequently, the deposition of a proper amount of release agent on the imaging member is important for good image transfer, particularly in duplex printing operations.
With current arrangements utilizing a metering blade to control the thickness of the release agent on the imaging drum, more release agent is deposited on the drum as the speed of the drum increases. One way to address this is to keep the drum speed low, but this may also lower productivity. Another issue arising from the use of known metering blade arrangements is that the metering blades wear over time, causing excess release agent to remain on the imaging drum or causing an uneven layer of release agent on the imaging drum.
In view of the foregoing, it would be desirable to provide a printer drum maintenance system capable of controlling the thickness of the release agent on the imaging drum without lowering the productivity of the printer. It would also be desirable to provide a printer drum maintenance system capable of applying a consistent and even layer of release agent on the imaging drum even after extended periods of use of the printer.